It is well known to use sacrificial anodes to prevent corrosion of metallic bodies in corrosive environments, such as sea water. Such sacrificial anodes are typically metallic members which are mounted local to or on the body they are to protect and are more susceptible to galvanic corrosion in the given environment in which they are located and thus more anodic. As the sacrificial anode is more anodic (less noble) than the metal of the parent structure a small localised electrochemical cell is set up between the anode and the body which is to be protected when placed in an electrolyte such as sea water. In this way, corrosion of the metallic body is reduced, if not entirely prevented. The anodes are sacrificial in that they corrode during the process and require periodic replacement.
It is common practice to use surface mounted sacrificial anodes which are readily replaced when necessary. However, surface mounted sacrificial anodes represent a hydrodynamic penalty in the form of increased drag in conditions where the body is subjected to a constrained flow of water, such as a pipe or duct or in unconstrained flow such as on the rudder of a ship. The additional drag is generally undesirable.
One option for overcoming the hydrodynamic penalty is to use an impressed current cathodic protection system which utilises a permanent (non consumable) anode through which a current is passed during operation. This has the advantage that the anode can have a much reduced profile and represents a lower hydrodynamic penalty. However, the complexity and cost of such a system is too high for many applications.
The present invention seeks to provide a sacrificial anode which seeks to overcome some of the problems of the known systems.